Stand in the center of the unit and grip the each handle with your opposite arm (grip the left pully with your right arm and the right pully with your left arm). Place your feet about shoulder width apart and bend over at the waist until your body is parallel to the ground. Keeping your back flat and knees bent, raise the weights out to your sides until your upper arms are slightly higher than your shoulders. Lower the weight over the same path and continue until you reach muscular failure.
You should be in complete control of the weight at all times and it is very important that you avoid using jerky motions or body momentum to lift the weight. You'll have to go fairly light on this exercise in order to allow for a full range of motion and maximal stimulation of the rear shoulders.
Bent-Over Cable Rear Lateral Raise Shoulder Exercise - Start Position
Bent-Over Cable Rear Lateral Raise Shoulder Exercise - Finish Position